Process for the manufacture of methacrylic or acrylic acid

ABSTRACT

A catalyst comprising (1) palladium, (2) phosphorus, (3) antimony, (4) X and (5) oxygen wherein X denotes at least one element selected from the group consisting of potassium, sodium, rubidium, lithium, cerium, beryllium, magnesium, calcium, vanadium, strontium, zinc, thorium and rhenium. 
     There is also provided a process for the manufacture of methacrylic or acrylic acid by oxidizing methacrolein or acrolein with molecular oxygen in the vapor phase in the presence of the catalyst defined above.

This is a continuation of application Ser. No. 141,009 filed on Apr. 17, 1980, abandoned, which is a continuation of application Ser. No. 959,499 filed on Nov. 13, 1978, abandoned, which is a divisional application of Ser. No. 758,352 filed on Jan. 10, 1977, U.S. Pat. No. 4,138,365.

BACKGROUND OF THE INVENTION

This invention relates to a process for the production of methacrylic or acrylic acid by oxidizing methacrolein or acrolein and to a catalyst.

More particularly, this invention relates to a process for the production of methacrylic or acrylic acid by oxidizing methacrolein or acrolein with molecular oxygen in the presence of steam by using a catalyst comprising (1) palladium, (2) phosphorus, (3) antimony, (4) X and (5) oxygen wherein X denotes at least one element selected from the group consisting of potassium, sodium, rubidium, lithium, cerium, beryllium, magnesium, calcium, vanadium, strontium, zinc, thorium and rhenium, and to the catalyst.

The process of the invention may further comprise supplying into the reaction system a phosphoric acid or a phosphorus compound capable of forming a phosphoric acid through a chemical change during the reaction.

For the synthesis of methacrylic acid by oxidizing methacrolein in a vapor phase a number of catalysts have hitherto been proposed.

Almost all of these catalysts, however, have low activities. Further, if the reaction is carried out at an elevated temperatures in order to increase the conversion, large amounts of undesirable by-products such as carbon monoxide, carbon dioxide, acetic acid etc. are produced so that the per-pass yield of methacrylic acid is very low.

The catalysts as disclosed in the Japanese Patent Laid-Open Publication Nos. 67216/1973 and 61416/1973, which are improved in their catalytic activity and selectivity, comprise phosphomolybdic acid or its salts as a main ingredient.

Phosphomolybdic acid-based catalysts have a disadvantage that the catalyst lifetime is short. Once they lose activity, the activity of these catalysts cannot be restored by means of a simple treatment such as re-calcination, for example. When the temperature of reaction or calcination exceeds 450° C., they are abruptly degraded in catalytic activity. Thus, they are thermally unstable and they are not always available for commercial use.

Further, conventional phosphomolybdic acid-based catalysts offer a notably short catalytic lifetime when the reaction is carried out at a particularly high space velocity.

From a commercial aspect, it is desired to develop a catalyst which has acceptable activity and selectivity at low temperatures as well as a longer service life. Particularly desirable is a catalyst which can maintain its activity over a long period of time even when the reaction is carried out at high space velocities.

DESCRIPTION OF THE INVENTION

The inventors have made a study on the manufacture of methacrylic and acrylic acids, particularly on a catalyst suitable for their manufacture and the influence thereon, in order to obviate the above-described disadvantages of the prior art and have found a process for the production of methacrylic or acrylic acid from methacrolein or acrolein wherein not only the conversion of methacrolein or acrolein is high, but also the selectivity of methacrylic or acrylic acid produced is high at low temperatures and a novel catalyst therefor which has a longer service life even under the condition of a high space velocity.

According to the present invention, not only methacrolein or acrolein is susceptible to oxidation at low temperatures and methacrylic or acrylic acid is produced in high yields, but also the formation of by-products such as acetic acid, carbon monoxide and carbon dioxide owing to the degradation is well suppressed. In addition the catalyst according to the present invention is thermally stable and therefore has a substantially longer service life, particularly even when the reaction is carried out at high space velocities.

The catalyst of the present invention comprises (1) palladium, (2) phosphorus, (3) antimony, (4) X and (5) oxygen wherein X denotes at least one element selected from the group consisting of potssium, sodium, rubidium, lithium, cerium, beryllium, magnesium, calcium, vanadium, strontium, zinc, thorium and rhenium. The catalyst of the present invention has a long service life which is significantly superior to those of the prior phosphomolybdic acid-based catalysts.

It has suprisingly been found that the catalyst is stable at elevated temperatures, for example, at 600° C.

However, this catalyst as such is not completely satisfactory, because a part of phosphorus which is one of the essential components of the catalyst, though in a very small amount, leaves out of the catalyst system during the reaction. Consequently, the semi-eternal life required for commercial catalysts can not be attained.

The inventors have found that when the reaction is carried out in the presence of the catalyst, the catalyst can be stabilized and its service life can further be prolonged by continuously or intermittently supplementing phosphorus in an appropriate amount corresponding to that of the phosphorus which leaves out of the catalyst systems.

The process of the present invention is epoch-making and of great value for commercial use since methacrylic or acrylic acid can be selectively produced in high yields for long periods of time.

The term "a phosphoric acid or a phosphorus compound capable of forming a phosphoric acid through a chemical change during the reaction" (hereinafter to be referred to as a phosphorus-containing compound) which is to be supplied to the reaction system in accordance with the present invention means any of phosphoric acids and phosphorus compounds capable of forming a phosphoric acid through a chemical reaction such as hydrolysis, oxidation, etc., including orthophosphoric acid, phyrophosphoric acid, metaphosphoric acid, phosphorous acid, hypophosphorous acid, phosphine, organic phosphoric acids, solid phosphoric acids, etc.

To the reaction system the phosphorus-containing compound may be supplied in any suitable manner.

For example, if the phosphorus-containing compound is water-soluble, it may uniformly be dissolved in water to be used for the reaction so that it is carried to the reaction system along with water.

If the phosphorus-containing compound is solid, for example, a solid phosphoric acid, this solid material may be charged in front of the catalyst layer. As steam is fed and made contact with the charged material, the latter generates a phosphoric acid, which is carried to the catalyst layer along with steam.

Furthermore, if the phosphorus-containing compound is gaseous, a gaseous mixture of the same and air may be fed to the catalyst layer.

The amount of the phosphorus-containing compound to be supplied may vary over a wide range. In general, the phosphorus-containing compound is supplied so that the amount of phosphorus contained in the compound is preferably 5 to 1×10⁻⁴ wt%, more particularly 0.5 to 1×10⁻³ wt% on the basis of a total amount of water fed during the reaction.

A preferred catalyst according to the present invention has the following composition:

    Pd.sub.a P.sub.b Sb.sub.c X.sub.d O.sub.e

wherein X denotes at least one element selected from the group consisting of potassium, sodium, rubidium, lithium, cerium, beryllium, magnesium, calcium, vanadium, strontium, zinc, thorium and rhenium, the subscripts a, b, c, d and e denote the number of the Pd, P, Sb, X and O atoms, and wherein a is 1, b is 1 to 42, c is 0.1 to 15, d is 0.1 to 15 and e is a number determined by the valences of other elements and usually from 3.7 to 143.5.

A more preferred catalyst is a composition represented by the above formula in which the ratio among a, b, c, d and e lies in the following ranges: a:b:c:d:e=1:(1-28):(0.2-10):(0.1-10):(3.9-114.7).

The catalyst according to the present invention can be prepared in a conventional manner well known in the art, for example, by the following procedures.

In one case, compounds of respective constituent elements and the carrier, if a carrier is used, are mixed. The resultant mixture is evaporated to dryness and then the dried product is calcined.

In another case, a solid carrier is impregnated with compounds of respective constituent elements. This impregnated carrier is evaporated to dryness and then calcined.

In yet another case, a solid carrier is impregnated with compounds of some consituent elements and then subjected to a heat treatment, preferably at a temperature of 100°-800° C. The partly impregnated carrier is further impregnated with compounds of the remaining constituent elements. This twice impregnated carrier is evaporated to dryness and then calcined.

In any of the above-described procedures the calcination temperature lies preferably in a range of 300°-800° C., more preferably in a range of 350°-550° C.

If necessary, the calcination or the heat treatment may be carried out in an atmosphere of reducing agent such as hydrogen, hydrocarbon etc.

Examples of compounds of respective constituent elements are listed below.

Examples of palladium compounds include palladium chloride, nitrate and sulfate, palladium black and the like.

Examples of phosphorus compounds include orthophosphoric, pyrophosphoric, metaphosphoric, polyphosphoric, phosphorous and hypophosphorous acids and salts thereof and the like.

Examples of antimony compounds include oxides, hydroxides and chlorides of antimony such as antimony trioxide, trichloride and pentachloride and the like.

Examples of potassium, sodium, rubidium, lithium, cerium, beryllium, magnesium, calcium, vanadium, strontium, zinc, thorium and rhenium compounds include nitrates, hydrochlorides, phosphates, sulfates, oxides, hydroxides etc. of such elements.

More concrete procedures for the preparation of the catalyst are as follows.

To an aqueous ammonia solution of any suitable palladium salt, for example palladium chloride is added orthophosphoric acid, phosphorous acid, hypophosphorous acid or any other phosphoric acid or salt thereof, yielding a clean solution. To this clean solution are further added a soluion of salt of X compound, for example, magnesium nitrate or magnesium phosphate, and antimony compound such as antimony oxide, hydroxide or chloride, for example, antimony trioxide, yielding a mixture. Any suitable carrier is impregnated with the above-described mixture, evaporated to dryness and then calcined in air at 300°-800° C. for four or more hours.

The carrier which has been impregnated with a palladium compound such as palladium salt and thermally treated may be impregnated with a phosphorus compound, X compound and antimony compound and then calcined.

Or, the carrier which has been impregnated with X compound and antimony compound and thermally treated may be impregnated with an palladium compound and then calcined in air and thermally treated in an atmosphere of reducing agent. The resultant substance is impregnated with phosphorus compound and then calcined.

In any case the activity of the catalyst is not adversely affected.

The catalyst can include a carrier to lower the catalyst concentration, increase the catalyst strength or to enhance the economy of the catalyst.

As the carrier may be employed inert substances such as silica sol, silica gel, silicon carbide, α-alumina, Alundum, celite, boiling bubble stone, aluminum powder and the like.

The catalyst may be used in the form of spherical granules, pellets, particles crushed to suitable size, tablets etc.

Molecular oxygen is used for oxidizing methacrolein or acrolein in accordance with the present invention. To this end air is generally used. Pure oxygen may also be used alone or in admixture with an inert gas such as nitrogen, carbon dioxide and the like.

To the reaction system methacrolein or acrolein and oxygen are fed as a gaseous feed mixture in such proportions that the molar ratio of methacrolein or acrolein to oxygen is preferably 1:(0.5-30), more preferably 1:(1-8).

The reaction between methacrylein or acrolein and oxygen is carried out in the presence of steam according to the process of the present invention. The presence of steam is indispensable to this reaction. If steam is absent, the oxidation of methacrolein or acrolein may occur to a very small extent or may not occur at all. In this aspect the catalyst according to the present invention is virtually different from known catalysts used for the oxidation of methacrolein or acrolein.

The steam is involved in the gaseous feed mixture in such proportions that the amount of steam is preferably 0.5 to 40 moles, more preferably 1 to 28 moles per mole of methacrolein or acrolein.

The temperature for carrying out the reaction is not so critical. The reaction may preferably be carried out at a temperature of 180° to 420° C., especially 200° to 390° C.

The reaction can be carried out at atmospheric pressure or at lower or higher pressures. In general it is convenient to carry out the reaction at atmospheric pressure. A preferable range of pressure is 0.3 to 15 atm.

The gaseous feed mixture can be introduced at any desirable space velocity, preferably at a space velocity of 300 to 15,000 l-gas/l-cat.hr, especially 700 to 8,000 l-gas/l-cat.hr.

According to the present invention satisfactory results are obtained even when the reaction is carried out at space velocities as high as 2,000 to 8,000 l-gas/l-cat.hr. Further the service life of the catalyst is maintained for a long period of time under such conditions.

The catalyst of the present invention may be applied in any form selected from a fixed bed, a fluidized bed and a moving bed.

The following examples are illustrative of the catalyst and the process of the present invention. In the examples, the terms "conversion of methacrolein or acrolein", "selectivity of methacrylic or acrylic acid", "yield of methacrylic or acrylic acid", and "space velocity" are defined as follows.

EXAMPLE 1

While 16.0 g of Aerosil (SiO₂) was heated and agitated, 0.4 g of antimony trioxide and 0.17 g of magnesium phosphate were added.

The mixture was concentrated by heating, then evaporated to dryness and thereafter, dried at 100° C. for eight hours. The dried mixture was impregnated with an aqueous ammonia solution containing 0.44 g of palladium chloride, evaporated to dryness, thereafter repeatedly washed with 10 liters of distilled water and dried. The dried product was subjected to a heat treatment in the air at 450° C. for five hours and then thermally treated in an atmosphere of hydrogen at 450° C. for five hours. The product was impregnated with 6.5 g of hypophosphorous acid, evaporated to dryness. Thereafter, the dried product was calcined in the air at 450° C. for five hours. The thus obtained product is named Catalyst A, the composition of which is represented by the formula:

    Pd.sub.1 P.sub.12.3 Sb.sub.1 Mg.sub.0.5 O.sub.33.75

A reaction tube of stainless steel having an inner diameter of 20 mm was filled with 10 ml of Catalyst A and dipped in a bath of molten nitrate. With the use of this reaction tube filled with Catalyst A the oxidation of methacrolein was carried out for 120 days.

As the phosphorous-containing compound was used trimethyl phosphate in the form of a 0.1 % aqueous solution.

This aqueous solution was fed in an amount of 5 cc per hour.

A gaseous feed mixture contained methacrolein, oxygen, steam, nitrogen and phosphorus in a relative molar ratio of 1:2:14:18.1:1.8×10⁻³.

The gaseous feed mixture was supplied at a SV of 1565 l-gas/l-cat.hr.

The results of the reaction were as shown in Table 1. The yield of acrylic acid, acetic acid, carbon dioxide and carbon monoxide formed as the by-products in the conversion of methacrolein into methacrylic acid at the initial stage were 2.0%, 1.0%, 5.1% and 6.3%, respectively.

                  TABLE 1                                                          ______________________________________                                                                       Yield of                                                                              Selectivity                               Reaction                                                                               Temperature                                                                               Conversion meth-  of meth-                                  time    of the nitrate                                                                            of meth-   acrylic                                                                               acrylic                                   (day)   bath (°C.)                                                                         acrolein (%)                                                                              acid (%)                                                                              acid (%)                                  ______________________________________                                         Initial 300        78.5       64.5   82.2                                      stage                                                                           40     300        78.7       64.7   82.2                                      120     300        78.7       64.5   82.0                                      ______________________________________                                    

EXAMPLE 2

Example 1 was repeated except that metaphosphoric acid in the form of a 0.1% aqueous solution was used as the phosphorus-containing compound in place of trimethyl phosphate.

Other reaction conditions were the same as those of Example 1. The results are shown in Table 2.

                  TABLE 2                                                          ______________________________________                                                                      Yield of                                          Reaction                                                                              Temperature                                                                               Conversion meth-  Selectivity of                             time   of the nitrate                                                                            of meth-   acrylic                                                                               methacrylic                                (day)  bath (°C.)                                                                         acrolein (%)                                                                              acid (%)                                                                              acid (%)                                   ______________________________________                                         Initial                                                                               301        77.8       63.7   81.9                                       stage                                                                           40    301        77.9       63.5   81.5                                       120    301        77.9       63.7   81.8                                       ______________________________________                                    

The yield of acrylic acid, acetic acid, carbon dioxide and carbon monoxide formed as the by-products in the conversion of methacrolein into methacrylic acid at the initial stage were 3.1%, 1.0%, 5.0% and 6.0%, respectively.

EXAMPLE 3

A catalyst having the same composition as that of Example 1 was prepared similar to that of Example 1, except that hypophosphorous acid was replaced by phosphorous acid.

With the use of the catalyst the reaction was carried out in a similar manner as described in Example 1. The results are shown in Table 3.

                  TABLE 3                                                          ______________________________________                                         Reaction                                                                              Temperature                                                                               Conversion                                                                               Yield of                                                                               Selectivity of                             time   of the nitrate                                                                            of metha- methacrylic                                                                            methacrylic                                (day)  bath (°C.)                                                                         crolein (%)                                                                              acid (%)                                                                               acid (%)                                   ______________________________________                                         Initial                                                                               298        77.5      64.2    82.8                                       stage                                                                           40    298        76.7      64.1    83.6                                       120    298        77.6      64.3    82.8                                       ______________________________________                                    

The yield of acrylic acid, acetic acid, carbon dioxide and carbon monoxide formed as the by-products in the conversion of methacrolein into methacrylic acid at the initial stage were 1.0%, 0.5%, 5.3% and 6.5%, respectively.

EXAMPLE 4

The reaction described in Example 1 was repeated except that acrolein was used in place of methacrolein.

The results are shown in Table 4.

                  TABLE 4                                                          ______________________________________                                         Reaction                                                                              Temperature Conversion                                                                               Yield of                                                                               Selectivity                               time   of the nitrate                                                                             of acrolein                                                                              acrylic of acrylic                                (day)  bath (°C.)                                                                          (%)       acid (%)                                                                               acid (%)                                  ______________________________________                                         Initial                                                                               297         96.5      90.1    93.4                                      stage                                                                           40    297         96.7      90.0    93.1                                      120    297         96.7      90.4    93.5                                      ______________________________________                                    

The yield of acetic acid, carbon monoxide, carbon dioxide and acetone formed as the by-products in the conversion of acrolein into acrylic acid at the initial stage were 1.0%, 2.4%, 2.0% and 1.0%, respectively.

EXAMPLE 5

The reaction was carried out under the same conditions as those of Example 1, except that the phosphorus-containing compound was not fed at all. The results are shown in Table 5.

EXAMPLE 6

The reaction was carried out under the same conditions as those of Example 4, except that the phosphorus-containing compound was not fed at all. The results are shown in Table 5.

                  TABLE 5                                                          ______________________________________                                         Ex-           Tempera-  Conversion                                                                             Yield of                                                                              Selectivity                             am-  Reaction ture of   of meth-                                                                               meth-  of meth-                                ple  time     the nitrate                                                                              acrolein                                                                               acrylic                                                                               acrylic                                 No.  (day)    bath (°C.)                                                                        (%)     acid (%)                                                                              acid (%)                                ______________________________________                                         5    Initial  299       78.7    64.1   81.4                                         stage                                                                          10       299       77.9    61.3   78.7                                    ______________________________________                                         Ex-           Tempera-  Conversion                                                                             Yield of                                                                              Selectivity                             am-  Reaction ture of   of      acrylic                                                                               of acrylic                              ple  time     the nitrate                                                                              acrolein                                                                               acid   acid                                    No.  (day)    bath (°C.)                                                                        (%)     (%)    (%)                                     ______________________________________                                         6    Initial  296       95.5    89.7   93.9                                         stage                                                                          10       296       90.1    83.1   92.2                                    ______________________________________                                    

EXAMPLES 7-48

Catalysts having the compositions shown in Table 6 were prepared in a manner similar to that described in Example 1, if necessary, using nitrates of rubidium, calcium, potassium, lithium, zinc, sodium, strontium, thorium, cerium and beryllium, ammonium metavanadate and rhenium chloride. With use of these catalysts the reactions were carried out under the same conditions as those of Example 1, except that the phosphorus-containing compound was not fed at all. The results are shown in Table 6.

                                      TABLE 6                                      __________________________________________________________________________                    Temperature                                                                           Conversion  Selectivity                                  Exam-          of the ni-                                                                            of meth-                                                                             Yield of                                                                             of meth-                                     ple            trate bath                                                                            acrolein                                                                             methacrylic                                                                          acrylic acid                                 No. Catalyst composition                                                                      (°C.)                                                                          (%)   acid (%)                                                                             (%)                                          __________________________________________________________________________      7  Pd.sub.1 P.sub.1 Mg.sub.0.3 Sb.sub.1 O.sub.5.3                                            250    79.5  50.0  62.9                                          8  Pd.sub.1 P.sub.3 Mg.sub.0.5 Sb.sub.1 O.sub.10.5                                           252    76.5  45.3  59.2                                          9  Pd.sub.1 P.sub.9 Mg.sub.1.0 Sb.sub.2 O.sub.27.5                                           263    75.5  56.5  74.8                                         10  Pd.sub.1 P.sub.15 Mg.sub.5.0 Sb.sub.7 O.sub.54                                            271    74.5  61.7  82.8                                         11  Pd.sub.1 P.sub.28 Mg.sub.10 Sb.sub.10 O.sub.96                                            278    71.5  58.5  81.8                                         12  Pd.sub.1 P.sub.10 Mg.sub.0.1 Sb.sub.0.2 O.sub.26.4                                        270    73.5  51.3  69.7                                         13  Pd.sub.1 P.sub.12 Rb.sub.1 Sb.sub.1 O.sub.33.5                                            277    74.7  61.5  82.3                                         14  Pd.sub.1 P.sub.5 Rb.sub.0.5 Sb.sub.1 O.sub.15.3                                           269    76.3  55.4  72.6                                         15  Pd.sub.1 P.sub.18 Rb.sub.5 Sb.sub.4 O.sub.50                                              281    75.3  52.1  69.2                                         16  Pd.sub.1 P.sub.24 Rb.sub.1 Sb.sub.1 O.sub.63                                              281    74.5  57.3  76.9                                         17  Pd.sub.1 P.sub.12 Ca.sub.1 Sb.sub.1 O.sub.33.5                                            274    76.5  62.3  81.4                                         18  Pd.sub.1 P.sub.21 Ca.sub.0.5 Sb.sub.2 O.sub.57                                            285    74.5  59.1  79.3                                         19  Pd.sub.1 P.sub.23 Ca.sub.2 Sb.sub.3 O.sub.65                                              291    72.3  54.3  75.1                                         20  Pd.sub.1 P.sub.5 Ca.sub.0.2 Sb.sub.0.6 O.sub.14.6                                         271    75.5  49.1  65.0                                         21  Pd.sub.1 P.sub.13 K.sub.0.5 Sb.sub.1 O.sub.35.3                                           273    75.6  60.5  80.0                                         22  Pd.sub.1 P.sub.20 K.sub.1 Sb.sub.2 O.sub.54.5                                             275    74.5  55.2  74.1                                         23  Pd.sub.1 P.sub.10 K.sub.5 Sb.sub.2 O.sub.31.5                                             268    70.2  43.1  61.4                                         24  Pd.sub.1 P.sub.28 K.sub.9 Sb.sub.8 O.sub.87.5                                             285    76.0  41.0  53.9                                         25  Pd.sub.1 P.sub.12 Zn.sub.1 Sb.sub.1 O.sub.33.5                                            287    74.9  59.5  79.4                                         26  Pd.sub.1 P.sub.21 Zn.sub.2 Sb.sub.2 O.sub.58.5                                            290    73.9  57.5  77.8                                         27  Pd.sub.1 P.sub.12 Na.sub.1 Sb.sub.1 O.sub.33                                              273    74.5  60.7  81.5                                         28  Pd.sub.1 P.sub.21 Na.sub.0.5 Sb.sub.2 O.sub.56.8                                          282    77.0  59.6  77.4                                         29  Pd.sub.1 P.sub.26 Na.sub.5 Sb.sub.3 O.sub.73                                              290    77.5  43.5  56.1                                         30  Pd.sub. 1 P.sub.5 Na.sub.0.1 Sb.sub.0.5 O.sub.14.3                                        261    76.2  40.0  52.5                                         31  Pd.sub.1 P.sub.12 V.sub.0.5 Sb.sub.1 O.sub.33.3                                           267    73.5  62.2  84.6                                         32  Pd.sub.1 P.sub.21 V.sub.1 Sb.sub.3 O.sub.59.5                                             275    74.5  58.1  78.0                                         33  Pd.sub.1 P.sub.5 V.sub.0.2 Sb.sub.5 O.sub.21.3                                            263    72.6  40.1  55.2                                         34  Pd.sub.1 P.sub.12 Re.sub.1 Sb.sub.2 O.sub.36                                              250    77.5  63.1  81.4                                         35  Pd.sub.1 P.sub.23 Re.sub.2 Sb.sub.1 O.sub.64                                              260    78.2  60.1  76.9                                         36  Pd.sub.1 P.sub.6 Re.sub.0.3 Sb.sub.0.5 O.sub.17.4                                         241    75.6  53.2  70.4                                         37  Pd.sub.1 P.sub.12 Sr.sub.0.5 Sb.sub.1 O.sub.33                                            267    75.5  57.6  76.3                                         38  Pd.sub.1 P.sub.24 Sr.sub.3 Sb.sub.2 O.sub.67                                              278    73.1  56.9  77.8                                         39  Pd.sub.1 P.sub.5 Sr.sub.5 Sb.sub.0.5 O.sub.19.3                                           269    77.0  42.1  54.7                                         40  Pd.sub.1 P.sub.10 Th.sub.1 Sb.sub.1 O.sub.29.5                                            276    74.5  59.2  79.5                                         41  Pd.sub.1 P.sub.20 Th.sub.3 Sb.sub.3 O.sub.61.5                                            295    70.5  53.5  75.9                                         42  Pd.sub.1 P.sub.4 Th.sub.0.5 Sb.sub.2 O.sub.15                                             263    74.5  46.3  62.1                                         43  Pd.sub.1 P.sub.15 Ce.sub.1 Sb.sub.1 O.sub.40.5                                            279    74.3  57.5  77.4                                         44  Pd.sub.1 P.sub.20 Ce.sub.2 Sb.sub.5 O.sub.59.5                                            288    71.1  42.2  59.4                                         45  Pd.sub.1 P.sub.13 Be.sub.1 Sb.sub.1 O.sub.36                                              274    75.3  53.5  71.0                                         46  Pd.sub.1 P.sub.23 Be.sub.2 Sb.sub.2 O.sub.63.5                                            296    70.4  50.1  71.1                                         47  Pd.sub.1 P.sub.12 Li.sub.1 Sb.sub.0.6 O.sub.32.4                                          276    75.3  58.0  77.0                                         48  Pd.sub.1 P.sub.21 Li.sub.2 Sb.sub.1 O.sub.56                                              290    71.1  55.1  77.5                                         __________________________________________________________________________

EXAMPLES 49-61

Catalysts having the compositions shown in Table 7 were prepared in a manner similar to those described in Examples 7-48. With use of these catalysts the reactions were carried out under the same conditions as those of Example 1. The results are shown in Table 7.

                                      TABLE 7                                      __________________________________________________________________________                           Temperature                                                                           Conversion                                                                           Yield of                                                                            Selectivity                            Exam-            Reaction                                                                            of the ni-                                                                            of meth-                                                                             meth-                                                                               of meth-                               ple              time trate bath                                                                            acrolein                                                                             acrylic                                                                             acrylic acid                           No. Catalyst composition                                                                        (day)                                                                               (°C.)                                                                          (%)   acid (%)                                                                            (%)                                    __________________________________________________________________________     49  Pd.sub.1 P.sub.12 Rb.sub.1 Sb.sub.1 O.sub.33                                                0    277    74.7  61.5 82.3                                                    40   277    74.6  61.4 82.3                                                    120  277    74.6  61.5 82.4                                   50  Pd.sub.1 P.sub.12 Ca.sub.1 Sb.sub.1 O.sub.33.5                                              0    274    76.5  62.3 81.4                                                    40   274    76.6  62.2 81.2                                                    120  274    76.5  62.3 81.4                                   51  Pd.sub.1 P.sub.12 K.sub.0.5 Sb.sub.1 O.sub.35.3                                             0    273    75.6  60.5 80.0                                                    40   273    75.4  60.3 80.0                                                    120  273    75.5  60.6 80.2                                   52  Pd.sub.1 P.sub.12 Na.sub.1 Sb.sub.1 O.sub.33                                                0    273    74.5  60.7 81.5                                                    40   273    74.4  61.0 82.0                                                    120  273    74.6  60.8 81.5                                   53  Pd.sub.1 P.sub.12 V.sub.0.5 Sb.sub.1 O.sub.33.3                                             0    267    73.5  62.2 84.6                                                    40   267    73.4  61.9 84.3                                                    120  267    73.4  62.0 84.5                                   54  Pd.sub.1 P.sub.12 Re.sub.1 Sb.sub.2 O.sub.36                                                0    250    77.5  63.1 81.4                                                    40   250    77.5  62.9 81.2                                                    120  250    77.4  63.1 81.5                                   55  Pd.sub.1 P.sub.12 Sr.sub.0.5 Sb.sub.1 O.sub.33                                              0    267    75.5  57.6 76.3                                                    40   267    75.6  57.7 76.3                                                    120  267    75.6  57.8 76.5                                   56  Pd.sub.1 P.sub.10 Th.sub.1 Sb.sub.1 O.sub.29.5                                              0    276    74.5  59.2 79.5                                                    40   276    74.4  59.2 79.6                                                    120  276    74.5  59.1 79.3                                   57  Pd.sub.1 P.sub.15 Ce.sub.1 Sb.sub.1 O.sub.40.5                                              0    279    74.3  57.5 77.4                                                    40   279    74.1  57.3 77.3                                                    120  279    74.2  57.4 77.4                                   58  Pd.sub.1 P.sub.13 Be.sub.1 Sb.sub.1 O.sub.36                                                0    274    75.3  53.5 71.0                                                    40   274    75.3  53.6 71.2                                                    120  274    75.3  53.5 71.0                                   59  Pd.sub.1 P.sub.12 Li.sub.1 Sb.sub.0.6 O.sub.32.4                                            0    276    75.3  58.0 77.0                                                    40   276    75.4  58.2 77.2                                                    120  276    75.4  58.1 77.1                                   60  Pd.sub.1 P.sub.12.3 Sb.sub.1 Mg.sub.0.5 Rb.sub.0.5 O.sub.34                                 0    297    77.6  61.1 78.7                                                    40   297    77.5  61.2 78.9                                                    120  297    77.6  61.0 78.6                                   61  Pd.sub.1 P.sub.12 Sb.sub.0.7 V.sub.0.5 K.sub.0.2 O.sub.33.4                                 0    271    74.5  60.0 80.5                                                    40   271    74.4  60.0 80.6                                                    120  271    74.5  60.2 80.8                                   __________________________________________________________________________

EXAMPLES 62-73

The reactions described in Example 4 were repeated except that catalysts having the compositions shown in Table 8 prepared in the same manner as in Examples 7-48 were used and the phosphorus-containing compound was not fed at all. The results are shown in Table 8.

                                      TABLE 8                                      __________________________________________________________________________                   Temperature                                                                           Conversion                                                                           Yield of                                                                             Selectivity                                   Exam-         of the ni-                                                                            of acro-                                                                             acrylic                                                                              of acrylic                                    ple           trate bath                                                                            lein  acid  acid                                          No. Catalyst composition                                                                     (°C.)                                                                          (%)   (%)   (%)                                           __________________________________________________________________________     62  Pd.sub.1 P.sub.12 Rb.sub.1 Sb.sub.1 O.sub.33.5                                           291    95.0  89.1  93.8                                          63  Pd.sub.1 P.sub.12 Ca.sub.1 Sb.sub.1 O.sub.33.5                                           296    94.2  88.5  93.9                                          64  Pd.sub.1 P.sub.13 K.sub.0.5 Sb.sub.1 O.sub.35.3                                          300    94.3  87.5  92.8                                          65  Pd.sub.1 P.sub.12 Na.sub.1 Sb.sub.1 O.sub.33.5                                           297    95.0  88.0  92.6                                          66  Pd.sub.1 P.sub.12 V.sub.0.5 Sb.sub.1 O.sub.33.8                                          299    96.0  89.7  93.4                                          67  Pd.sub.1 P.sub.12 Re.sub.1 Sb.sub.1 O.sub.33.5                                           289    97.0  90.0  92.8                                          68  Pd.sub.1 P.sub.12 Sr.sub.0.5 Sb.sub.1 O.sub.33                                           291    94.5  87.9  93.0                                          69  Pd.sub.1 P.sub.10 Th.sub.1 Sb.sub.1 O.sub.29.5                                           288    95.6  88.5  92.6                                          70  Pd.sub.1 P.sub.15 Ce.sub.1 Sb.sub.1 O.sub.40.5                                           283    90.5  85.9  96.0                                          71  Pd.sub.1 P.sub.13 Be.sub.1 Sb.sub.1 O.sub.36                                             291    97.0  89.0  91.8                                          72  Pd.sub. 1 P.sub.12 Zn.sub.1 Sb.sub.2 O.sub.33.5                                          289    96.5  87.6  90.8                                          73  Pd.sub.1 P.sub.12 Li.sub.1 Sb.sub.0.6 O.sub.32.4                                         282    95.7  88.1  92.1                                          __________________________________________________________________________

EXAMPLE 74

The reactions described in Example 4 were carried out for 120 days using the same catalysts as in Examples 62-73. The results obtained after 120 days were nearly the same as those obtained at the initial stage. The yields of acrylic acid were not decreased for 120 days.

EXAMPLE 75

Examples 1 and 4 were repeated except that solid phosphoric acid (celite/phosphorus=50/50) heat treated at 550° C. was used as the phosphorus-containing compound in place of trimethyl phosphate.

On the upper side of the catalyst layer consisting of 10 ml of Catalyst A was placed 5 ml of the solid phosphoric acid.

The results were nearly the same as those of Examples 1 and 4.

EXAMPLE 76

Examples 49-61 and 74 were repeated except that orthophosphoric acid, metaphosphoric acid, pyrophosphoric acid and solid phosphoric acid were used as the phosphorus-containing compound in place of trimethyl phosphate, respectively, in each case. It has been found that the results are nearly the same as those of Examples 49-61 and 74.

EXAMPLE 77

Examples 1 and 4 were repeated except that the amount of the phosphorus-containing compound supplied was changed. The amount of phosphorus contained in the compound was changed in the range of 0.5 wt % to 1×10⁻³ wt % based on an amount of water fed. The results were nearly the same as those of Examples 1 and 4.

EXAMPLE 78

A catalyst was prepared by following the procedure noted in Example 1, except that the impregnation order of palladium and phosphorus was changed. Using this catalyst the reactions were carried out in the same manner as in Examples 1 and 4. The results were nearly the same as those of Examples 1 and 4.

EXAMPLE 79

A catalyst was prepared by following the procedure noted in Example 1, except that palladium and phosphorus were impregnated at the same time. Using this catalyst the reactions were carried out in the same manner as in Examples 1 and 4. The results were nearly the same as those of Examples. 1 and 4.

EXAMPLE 10

16.0 g of Aerosil, 0.4 g of antimony trioxide, 0.17 g of magnesium phosphate, 6.5 g of hypophosphorous acid and 10 cc of an aqueous ammonia solution containing 0.44 g of palladium chloride were mixed together. The mixture was evaporated to dryness. The dried product was calcined in the air at 450° C. for five hours. The catalyst thus obtained had a composition represented by the formula: Pd₁ P₁₂.3 Sb₁ Mg₀.5 O₃₃.75. Using this catalyst the reactions were carried out in the same manner as in Examples 1 and 4. The results were nearly the same as those of Examples 1 and 4.

EXAMPLE 81

Example 1 was repeated except that the gaseous feed mixtue was supplied at a SV of 4000 l-gas/l-cat.hr. The results are shown in Table 9.

                  TABLE 9                                                          ______________________________________                                         Reaction                                                                              Temperature                                                                               Conversion                                                                               Yield of                                                                               Selectivity                                time   of the nitrate                                                                            of metha- methacry-                                                                              of methacryl-                              (day)  bath (°C.)                                                                         crolein (%)                                                                              lic acid (%)                                                                           ic acid (%)                                ______________________________________                                         Initial                                                                               315        74.5      61.3    82.3                                       stage                                                                           40    315        74.4      61.2    82.2                                       120    315        74.5      61.4    82.4                                       ______________________________________                                    

EXAMPLE 82

Example 4 was repeated except that the gaseous feed mixture was supplied at a SV of 4000 l-gas/l-cat.hr. The results are shown in Table 10.

                  TABLE 10                                                         ______________________________________                                         Reaction                                                                               Temperature                                                                               Conversion                                                                               Yield of                                                                              Selectivity of                             time    of the nitrate                                                                            of acrolein                                                                              acrylic                                                                               acrylic acid                               (day)   bath (°C.)                                                                         (%)       acid (%)                                                                              (%)                                        ______________________________________                                         Initial 307        92.1      86.2   93.6                                       stage                                                                           40     307        92.3      85.9   93.1                                       120     307        92.2      86.0   93.3                                       ______________________________________                                     

What is claimed is:
 1. A process for the production of methacrylic or acrylic acid by the oxidation of methacrolein or acrolein with molecular oxygen in the presence of steam in the vapor phase by using a catalyst consisting essentially of the following composition:

    Pd.sub.a P.sub.b Sb.sub.c X.sub.d O.sub.e

wherein X denotes at least one element selected from the group consisting of potassium, sodium, rubidium, lithium, cerium, beryllium, magnesium, calcium, vanadium, strontium, zinc, thorium and rhenium, the subscripts a, b, c, d and e denote the number of the Pd, P, Sb, X and O atoms, and whrein a is 1, b is 1 to 42, c is 0.1 to 15, d is 0.1 to 15 and e is a number determined by the valences of the other elements and is from 3.7 to 143.5.
 2. A process according to claim 1 wherein a is 1, b is 1 to 28, c is 0.2 to 10, d is 0.1 to 10 and e is 3.9 to 114.7.
 3. A process according to claim 1 wherein a phosphoric acid or a phosphorus compound capable of forming a phosphoric acid through chemical change during the reaction is concurrently supplied to the reaction system.
 4. A process according to claim 3 wherein said phosphoric acid is orthophosphoric acid, pyrophosphoric acid or metaphosphoric acid.
 5. A process according to claim 3 wherein said phosphorus compound capable of forming a phosphoric acid through chemical change during the reaction is solid phosphoric acid or an organic phosphoric acid. 